5.7x28 AR upper, why not?


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bikemutt
July 6, 2014, 10:53 PM
I've noticed affordable (<$600) AR15 uppers available in the FN 5.7x28 round, pistol and rifle lengths. Ammo appears to be generally available, maybe easier to find than 22lr, for around $.48/round or so.

I don't own the FN pistol but I have shot one, it was lots of fun, and lots of polymer to be sure.

So, why not? Purpose: range toy.

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trigga
July 6, 2014, 11:02 PM
i never was attracted to the pistol caliber carbines unless you were restricted to say a pdw and concealment is key. i still think the 223/5.56 is a better caliber to have around and plenty on the shelf by now plus a wide variety of ammo for it.

Walkalong
July 7, 2014, 07:40 AM
As a range toy:

I had one, and reloaded for it for a short time, but it just bored me. The caliber would be more fun/useful in a bolt gun or Contender IMHO. The upper was heavy for such a small caliber. I would just as soon shoot my .22 LR AR. Too bad there isn't one readily available in .22 Mag.

I enjoyed my 9MM AR a great deal more, it is simpler (A great deal simpler) to reload, factory ammo is cheaper, brass is plentiful.... I could go on and on.

As a range toy it simply did not make the cut. :)

bracer
July 7, 2014, 08:20 AM
The 5.7 X 28 MM cartridge bullet energy fits between the 22 WMR and 22 Hornet when fired from a rifle length barrel. I m not a semi auto fan but should I find a used short bolt action rifle that could be re barreled with a 5.7X28 MM chamber I may get it. Should you find an upper for your AR rifle get it and enjoy.

Ohen Cepel
July 7, 2014, 08:26 AM
Instead of asking why not, you may want to ask why.

It's a neat round for its intended purpose and the platform carries a lot of ammo. However, expensive to plink with in my mind and I think ammo in the long term may be a bit of an issue.

Sam1911
July 7, 2014, 08:32 AM
One of my regulars had one and would shoot it in some of our carbine matches, but it really ... REALLY ... seemed that the only single thing it did better than a 5.56mm carbine was hold 50 rds. in a convenient and interesting magazine. (That was slower to swap out than a standard 30-rd mag, so a bit of a wash.)

If you were already heavily invested in that round, I could maybe see getting one. Otherwise, naaaaaah.

Trent
July 7, 2014, 09:00 AM
You'd lose a lot of benefits of the PS90 platform by going with an AR upper. I know it's cheaper to go the upper route, but the main draw of the PS90 is ergonomics, light weight, and (most importantly) the bullpup deisgn. It's extremely compact.

(Not to mention, accurate, but if the AR upper mfg. knows their business on barrels, that'll be a wash).

Since the ergonomics in the upper are going to be the same as the parent platform (AR-15), you really need to compare what you're gaining or losing against an AR upper. You aren't switching weapons platforms, you are converting an existing one.

Ability to shoot a new caliber? Great, *but* it's one that has historically been kind of hard to locate ammo for at times (now is not one of those times, fortunately, I just picked up 1500 rounds of Fiocci last week and got to comparison shop from vendors with it in stock).

Ability to hold more ammo? Great.. but you can do the same thing in a conventional AR with a beta mag. And... (hate to sound like an anti-gunner here), but you have to ask yourself "do I really need the extra X number of rounds?" With the cost of ammo, you're talking about burning $25 per 50 round magazine. That's not cheap. (Same cost as most 223 ammo).

But I reload...! Well, so do I... and the 5.7x28mm is no joy to reload. You have a dramatically reduced projectile selection over a 223 cartridge, a very narrow band of suitable powder burn rates (powder is still hard to find in some areas), etc. I looked for quite a long time before finding projectiles and suitable powder to use last year. On top of that, the cartridge is a persnickety little bugger to reload. Not at all like other rifle rounds.

Now.. if you already have a pistol and simply want to be able to use the same cartridge to reach out to 200 yards, go for it! (It is perfectly capable of remaining very accurate out to 200; I've won sporting rifle matches with a PS90 before. At 300 yards it's dropping like a meteor though, much more difficult to score hits, but still possible)

barnbwt
July 7, 2014, 09:01 AM
Ammo availability has been a "long term concern" going on 30 years, now. There are multiple manufacturers and a ton of guns in the caliber, and more sold every day. No, it won't be as common as 223 unless NATO adopts it, but neither are many other popular calibers.

TCB

MachIVshooter
July 7, 2014, 10:29 AM
I could see it in the same role as a .22 Hornet for varmint/predator control in areas that are a bit too populated for the much louder .22 centerfires .223 & up, areas which do not need the range of the larger cartridges but may have shots which are really pushing the limits of rimfire rounds. The Hornet definitely has an edge over the .22 mag and is not a whole lot louder; the 5.7x28 would offer that same low noise with increased performance, plus being able to use an autoloader that conveniently catches it's own brass.

Other than that application, though, I see the 5.7 AR upper as basically useless.

Trent
July 7, 2014, 11:03 AM
Ammo availability has been a "long term concern" going on 30 years, now. There are multiple manufacturers and a ton of guns in the caliber, and more sold every day. No, it won't be as common as 223 unless NATO adopts it, but neither are many other popular calibers.

TCB

It *would* have been adopted by NATO if H&K hadn't successfully lobbied Germany to block it. The vast majority of countries chose 5.7x28mm over H&K's 4.6mm round.

NATO standardization isn't the begin-and-end-all of any given cartridge. Sure it can go a long way to rapidly making acceptance, world wide. But even without it, the 5.7x28 has gained quite a lot of commercial and government acceptance throughout the world. Enough to keep the production lines running for a very long time (particularly since they can be easily converted from producing 223 to 5.7x28mm or back again).

It's not a mainstream cartridge, but it's on the brink of becoming one (several local stores stock it now).

You won't ever likely see stockpiles of cheap 5.7x28mm surplus hitting the market (at least not in our lifetimes), but still, I don't think finding ammo will be a problem beyond the occasional panic sprees we tend to have in the US...

barnbwt
July 7, 2014, 12:00 PM
It's got a lot better shot than 4.6x30 at going mainstream, at least :D. Given its sensitivity, I don't think I'd even want 40 year old surplus 5.7 :eek:

TCB

mavracer
July 7, 2014, 12:15 PM
Yes I gotta ask why. 5.56 is cheaper all around.

Trent
July 7, 2014, 02:01 PM
It's got a lot better shot than 4.6x30 at going mainstream, at least :D. Given its sensitivity, I don't think I'd even want 40 year old surplus 5.7 :eek:

TCB

The old white box SS195 "lead free" wasn't shelf stable anyway. The lead-free primers become inert after 7-10 years.

Not sure about the SS197SR, but long term storage hasn't been a concern yet. I've got 10 year old SS197SR that shoots fine still. (Not MUCH of it, but I've earmarked some boxes to hold back and shoot every couple of years just to satisfy my curiosity.)

barnbwt
July 7, 2014, 05:47 PM
Yes I gotta ask why. 5.56 is cheaper all around.
I would agree there's no point, if someone loaded "mouse-fart" 223 such that a small carbine (or SBR) would not make the gods flinch in pain when fired, especially indoors. Just as there is a use for 38spl over 357 in certain scenarios, such is the case for 5.7. A true pistol platform situation makes the need for something less powerful than 223 blantantly obvious, a PDW fairly obvious, and an AR upper even less obvious --the need is still there though, if you intend the carbine for lesser roles than to which 223 is suited. And don't forget that you do get a very impressive mag capacity without any protrusions besides the pistol grip (it just occurred to me that an ARES SCR somehow modded to use a 57 upper and SBR'd would be pretty dang slick and handy)

What I'd like even better would be for that dude on barfcom to manufacture and market his direct impingement AR modification to 5.7 --that'd be something neat, for sure, and a boon to reloaders of the round. Apparently it has enough oomph to rock a pistol-length gas system (with 16" barrel) with a lightweight buffer & spring.

TCB

Trent
July 8, 2014, 12:41 PM
Barn raises an interesting point that hasn't been raised before.

I keep the PS90 ready to go for wife & kids for home defense, since it's so easy to handle and fast / intuitive to operate.

Firing a 223 indoors is a very unpleasant experience when you don't have time to put on ears.

Firing a 5.7x28 is still a shock, but much less of one. Also risk of over penetration in apartments/close together housing is much less of a concern. (We have 5 kids, 3 dogs, 4 cats, so over penetration is a serious concern here at my place.)

Cooldill
July 8, 2014, 01:09 PM
I think the 5.7 rounds is probably the best thing going right now.

Small, lightweight, effective to 200 yards in rifles AND handguns, devastating wound ballistics (think 5.56 fragmentation), light recoil, flat shooting, can easily defeat light body armor, it's pretty much a complete package.

I say go for it.

ClickClickD'oh
July 8, 2014, 01:34 PM
5.56 is cheaper all around.

Only if you buy the cheapest garbage .223/5.56, and then only by a few cents. 50 Rounds of bottom of the barrel .223/5.56 usually runs around $22-$24. Twice that for premium ammunition. I pay $23 for AE 5.7 and $27 for the SS197SR So, even in the best case scenario you really aren't saving much money at all.

I always wonder when people bring up the price of 5.7... have 1911s gone out of style again? Because .45acp and 5.7 are pretty much the exact same price.. but no one seems to complain about .45s being too much.

As for why? OP states it's going to be a range toy. When has any true shooter every turned away from a range toy because it's an oddity? Heck, I think most of us like it when people cluster around to see the weird gun your brought.

Why for real use? Because you get less noise and recoil than a 5.56 with the same familiar controls on the AR lower. Bonus points for not having to bounce brass off walls, people and other things. Mag swaps are a little slower than a standard AR (faster with the Gen 2 uppers), but seriously... if you find yourself in a home defense situation where you've gone through 50 and need more... that's a bad bad night.

Here's my SBR Gen 2:

http://i142.photobucket.com/albums/r100/mdorbust/57s.jpg

I've taken a couple of small hogs and a coyote on the ranch with it. Did just fine. Know the guns limits and it will do just fine. If you need a magnified optic to see the target, you probably need another gun to shoot it. If it's going to be up close and personal, no problem.

mavracer
July 8, 2014, 01:50 PM
Only if you buy the cheapest garbage .223/5.56, and then only by a few cents. 50 Rounds of bottom of the barrel .223/5.56 usually runs around $22-$24. Twice that for premium ammunition. I pay $23 for AE 5.7 and $27 for the SS197SR So, even in the best case scenario you really aren't saving much money at all.
Well since I saved $200 on the upper and my mags cost 1/4 as much I'd say it's gonna take a long time for your ammo non savings to catch up.

And if 5.56 recoil bothers you................................ damn THR rules.

wally
July 8, 2014, 02:02 PM
Only if you buy the cheapest garbage .223/5.56, and then only by a few cents. 50 Rounds of bottom of the barrel .223/5.56 usually runs around $22-$24

I'd hardly call 2 moa ammo garbage, I was in Academy this morning and they had Monarch steel cased ammo for $6/20, that is $15/50, your rationalization is using bad data.

I'm not against the 5.7, in fact I have the AR57 upper and a PS90, but ammo cost is definitely a negative for it. I picked up several thousand rounds way back when Sportsman's guide was selling it for ~$18/50 which was still well above non-premium 5.56 back then.

ClickClickD'oh
July 8, 2014, 02:03 PM
Well since I saved $200 on the upper...

Ah well, I was going to put this 5.56 upper on my SBR lower, but it's $1,100... So I saved $500 going with the 5.7 (http://www.midwayusa.com/product/464559/daniel-defense-ar-15-pistol-mk18-a3-flat-top-upper-assembly-556x45mm-nato-1-in-7-twist-103-government-barrel-chrome-lined-cm-with-mk18-ris-ii-quad-rail-free-float-handguard-flash-hider?cm_vc=ProductFinding)

See how that works?

Now, were we talking ammo costs or complete weapon system costs... Because I've never seen a 5.7 system for $2K+, but I can find that in 5.56 all day. So, let's not try to play the "5.7 weapons systems are more expensive than 5.56 weapon systems" game.

And if 5.56 recoil bothers you................................ damn THR rules.

When out of facts to argue, Ad Hominem is always the best choice.

To help you along here, when I'm on foot in the heavy cedars, I use a Marlin 1895G loaded with 405gr bullets on top of 48gr of RL7. So no, 5.56 recoil doesn't bother me.

But my wife, who has access to the same firearms and sleeps in the same bed is 4'9".

ClickClickD'oh
July 8, 2014, 02:07 PM
I'd hardly call 2 moa ammo garbage, I was in Academy this morning and they had Monarch steel cased ammo for $6/20, that is $15/50, your rationalization is using bad data.

You know that Monarch is just Privi (brass) or Barnul (steel) brand ammo manufactured for sole distribution at Academy locations right?

I wouldn't hold it up as anything other than what it is, cheap com-bloc import.

wally
July 8, 2014, 02:17 PM
I wouldn't hold it up as anything other than what it is, cheap com-bloc import. I know, but it generally shoots 2moa in my ARs which is pretty much the accuracy spec of what gets issued to the troops.

I shoot lots of it at steel plates, I liked it even better back when it was $3/20 :)

Trent
July 8, 2014, 02:20 PM
To help you along here, when I'm on foot in the heavy cedars, I use a Marlin 1895G loaded with 405gr bullets on top of 48gr of RL7. So no, 5.56 recoil doesn't bother me.

But my wife, who has access to the same firearms and sleeps in the same bed is 4'9".

Agreed. My wife has serious trouble with 9mm recoil, even from a full size gun that dampens it down some, she's just too small. She carries a 380 ACP in her purse, about the most recoil she can handle. I've got a 38 special tucked away in the kitchen for her with mellow loads that she's good with too. (Figure bad guy isn't going to really care if he's hit at 800 fps vs 950fps... him getting hit in the first place is more important at the moment..)

223 recoil isn't bad *but* the noise when fired indoors is absolutely horrid. Muzzle flash can be eliminated with a Smith Vortex flash suppressor, but still, it's like hitting yourself with the sonic part of a flashbang. (M-8 stun grenade is ~170 decibels, a 20" AR is 160-165db, and it gets MUCH louder from a 16" or 14.5" tube.)

Conversely, a 10.5" PS90 is 158db, and it gets MUCH quieter as you move to the standard 16" barrel.

16" PS90 is still not hearing safe, but it's at least well below the threshhold of a damn flashbang grenade going off less than 2 feet in front of your face in an enclosed space. Which is essentially what your'e doing when you shoot an AR15 223 indoors.

Walkalong
July 8, 2014, 03:21 PM
They got it right with the PS90. It is the way to go (IMHO) if you want a semi auto rifle in 5.7.

As a range toy the AR 57 worked just fine, was cool and folks liked to shoot it, and was also quite accurate, but it just didn't fill a void for me.

It is well made, dependable, and if a fellow wants one and has the jack, heck they should try it. It just wasn't for me. I like my .22 LR AR, and love my 9MM AR, and just couldn't get excited about a caliber with a pretty good crack and not much oomph. I just don't need something between .22 LR and 9MM in the AR. Unless of course I could get on in .22 Mag. I know that sounds contradictory, and maybe it is, but I just have an affinity for .22 Mag and don't have to go through the trouble to load it. Loading 5.7 for blowback actions is a real pain.

MistWolf
July 8, 2014, 03:31 PM
I don't need the extra power of devastation the P90 give the 5.7 as I don't plan on ever travelling to a far off planet to mow down ranks of Jaffa. It's performance from an AR57 upper is plenty and I'd like to have one for no other reason than it sounds like a lot of fun. I wish I'd bought one when it was on sale for under $500. The 5.7 is a practical round- more so than the 22 mag.

I wonder if Ruger can be convinced to chamber a 77/22 style rifle in 5.7?

Cooldill
July 8, 2014, 03:32 PM
Agreed. My wife has serious trouble with 9mm recoil, even from a full size gun that dampens it down some, she's just too small. She carries a 380 ACP in her purse, about the most recoil she can handle. I've got a 38 special tucked away in the kitchen for her with mellow loads that she's good with too. (Figure bad guy isn't going to really care if he's hit at 800 fps vs 950fps... him getting hit in the first place is more important at the moment..)

223 recoil isn't bad *but* the noise when fired indoors is absolutely horrid. Muzzle flash can be eliminated with a Smith Vortex flash suppressor, but still, it's like hitting yourself with the sonic part of a flashbang. (M-8 stun grenade is ~170 decibels, a 20" AR is 160-165db, and it gets MUCH louder from a 16" or 14.5" tube.)

Conversely, a 10.5" PS90 is 158db, and it gets MUCH quieter as you move to the standard 16" barrel.

16" PS90 is still not hearing safe, but it's at least well below the threshhold of a damn flashbang grenade going off less than 2 feet in front of your face in an enclosed space. Which is essentially what your'e doing when you shoot an AR15 223 indoors.

Well, if you say so it must be true. :rolleyes:

Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting. This protects the hearing and many people say they "never heard the shot" if/when they do have to shoot in a home. I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.

MistWolf
July 8, 2014, 03:43 PM
But it doesn't protect your ears from being damaged

ClickClickD'oh
July 8, 2014, 03:43 PM
Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting.

People CAN experience auditory exclusion during high stress events. It is not a guaranteed physiological reaction nor is it guaranteed to repeat in people who have experienced it before. In fact, the opposite may occur and you may experience increase hearing perception.

This protects the hearing...

No, auditory exclusion certainly does not protect hearing. Physical hearing damage still occurs. The brain simply ignores input from certain non-critical functions to increase processing power for more critical functions.

I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.

Do you know anyone that's actually discharged a 7.5" SBR AR inside a home?

Sam1911
July 8, 2014, 03:57 PM
Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting. This protects the hearing and many people say they "never heard the shot" if/when they do have to shoot in a home. I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.I was about to jump on that and point out that it most certainly does nothing to protect your hearing, but it seems folks got to that point ahead of me.

:)

Cooldill
July 8, 2014, 04:12 PM
People CAN experience auditory exclusion during high stress events. It is not a guaranteed physiological reaction nor is it guaranteed to repeat in people who have experienced it before. In fact, the opposite may occur and you may experience increase hearing perception.



No, auditory exclusion certainly does not protect hearing. Physical hearing damage still occurs. The brain simply ignores input from certain non-critical functions to increase processing power for more critical functions.



Do you know anyone that's actually discharged a 7.5" SBR AR inside a home?
No but I personally know of several who use them in that roll. They are getting pretty popular as HD weapons.

Regardless if damage does occur or not, the amount of firing needed in that situation would not cause any lasting harm. Sure it might be noisy, but what gun isn't? The effectiveness of the platform far outweighs the fact that it might be louder than some weapons if fired indoors. My point still stands.

ClickClickD'oh
July 8, 2014, 04:25 PM
No but I personally know of several who use them in that roll. They are getting pretty popular as HD weapons.

How do they "use them in that roll"? Does that mean the AR sits under the bed or by the nightstand? Or does it mean that the people actively train with their AR to fill that roll in similar circumstances (shoot houses)? Because there's a hell of a lot of difference between someone who just picks a gun and sticks it under their bed and someone who has run it in the intended circumstances. I've run a 14.5 in a shoot house, and you damn well feel the thing in your chest. It's a loud beast even under plugs and muffs. I wouldn't want to toss off a 7.5 in a bedroom. Popping off an AR in a small room is not at all like popping one off on an open rifle range or even a large indoor bay.

Regardless if damage does occur or not, the amount of firing needed in that situation would not cause any lasting harm.

Do you have MD appended to your name?

If not, I think I'm going to take this guys word for it: Michael Stewart, PhD, CCC-A, Professor of Audiology, Central Michigan University - (http://www.asha.org/public/hearing/Recreational-Firearm-Noise-Exposure/)

"People who do not wear hearing protection while shooting can suffer a severe hearing loss with as little as one shot, if the conditions are right."

Cooldill
July 8, 2014, 04:48 PM
How do they "use them in that roll"? Does that mean the AR sits under the bed or by the nightstand? Or does it mean that the people actively train with their AR to fill that roll in similar circumstances (shoot houses)? Because there's a hell of a lot of difference between someone who just picks a gun and sticks it under their bed and someone who has run it in the intended circumstances. I've run a 14.5 in a shoot house, and you damn well feel the thing in your chest. It's a loud beast even under plugs and muffs. I wouldn't want to toss off a 7.5 in a bedroom. Popping off an AR in a small room is not at all like popping one off on an open rifle range or even a large indoor bay.



Do you have MD appended to your name?

If not, I think I'm going to take this guys word for it: Michael Stewart, PhD, CCC-A, Professor of Audiology, Central Michigan University - (http://www.asha.org/public/hearing/Recreational-Firearm-Noise-Exposure/)

"People who do not wear hearing protection while shooting can suffer a severe hearing loss with as little as one shot, if the conditions are right."
All I know is they own and use them for personal defense.

Some of the guys I talk with have been in REAL firefights in Afghan and Iraq.

I think they know what they're doing. Just sayin'.

ClickClickD'oh
July 8, 2014, 06:53 PM
All I know is they own and use them for personal defense.

So, you don't even know if a third party has ever actually fired the weapon in a close indoor environment, but you are willing to personally testify about what the effects of doing so would be?

Some of the guys I talk with have been in REAL firefights in Afghan and Iraq.

I think they know what they're doing. Just sayin'.

Then they weren't running 7.5s. They were either running 14.5s (where in this thread have we seen this number before?) or 20s. They also might not have ever run them indoors and they were most certainly doing so with earpro on.

So go ask your friends if they ever fired their M4s in a 12x12 room and how that went for them.

barnbwt
July 9, 2014, 12:53 AM
Also, I believe the savvy cool kids doing entry work would get some suppressors along with their full auto SBR's ;)

A braked 16" barrel is bad enough to be alongside of (you feel it in your sinuses and eyeballs). I have to assume a 7.5 is quite literally as violent as being boxed in the ears. You may not "hear" the bang, but you sure as hell won't hear anything afterward, either.

Well, except for "EEEEEEEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee...:

But only until your get your perforated eardrums stitched back up ;). I fired my five-seven without ears once in an enclosure. As best I recall, I perceived it as "wWOP!" followed by about ten to fifteen seconds of silence, then a gradual return of volume accompanied by temporary tinnitus and auditory sensitivity for about three days or so. A 223 is a good 25% more pressure, and a hell of a lot more gas volume behind the detonation bubble. An SBR AR15 would likely engulf your entire head in the overpressure bubble.

Also worth noting that a 5.7x28 may in fact be nearly equaling 223 in performance in that type of barrel length (I forget where they actually cross), and with ~1/2 the powder flash and blast.

TCB

MachIVshooter
July 9, 2014, 01:04 AM
Also worth noting that a 5.7x28 may in fact be nearly equaling 223 in performance in that type of barrel length (I forget where they actually cross), and with ~1/2 the powder flash and blast.

Not even close. A 55 gr 5.56mm ball round will still hit 2,500-2,600 FPS from a 7.5" tube. The 5.7x28 can't even manage that speed with half the bullet and an extra 3" of barrel.

The two rounds never cross on the performance scale.

Trent
July 9, 2014, 10:53 AM
Had a negligent discharge once in my early 20's.

Rifle was leaned up against the counter (top facing me), loaded magazine was sitting on top of the counter. Brain said "magazine is out, check the chamber." So I picked it up, put the buttstock on the counter - muzzle was MAYBE 9" in front of my nose. Jack the slide, round flew out, pull the trigger. I skipped the step of checking if it HAD a magazine in it because I saw a loaded one sitting next to it and *assumed* it had already been removed. When... in fact.. there were two magazines; one in the gun and one on the counter. :(

Saw white flash, couldn't hear anything. Buddy of mine came running in from the other room and grabbed my shoulders, turned me towards him. He's yelling SOMETHING at me, can see his lips moving but I can't hear a damn THING. I lip read "are you OK" and say (yell?) back "YES". Hand him the gun and say "I THINK I SHOT THE CEILING." Had a bloody nose, eyes were watering something fierce. Quite a shock.

Anyway about 15 minutes later I start hearing eeeeeeeeeeeeeeeeeeeeeeeeeeeee... about 30 minutes later EEEEEEEEEEEEEEEEEEEEEEEE... for several days ANY loud noises physically hurt and most noises had a really odd sound to them. One shot and I'd permanently damaged my hearing - I still have tinnitus.

That was one shot, in a large kitchen, with the windows and doors open (summertime) which allowed overpressure to vent a little. If the volume of space had been any smaller ....

Anyway when I say that ANY rifle (223, 7.62x39, 308, etc) is bad news when fired indoors, and that the results are similar to a flashbang on your fragile human system, I'm not joking around about it. Between the volume of gas you are venting, the equivalent loudness between an M-8 stun grenade and the various intermediary cartridge rifle platforms, the effect isn't too dissimilar.

I don't care if you only fire one shot, I don't care if you get auditory exclusion and don't hear it (I didn't), you WILL damage your hearing, and (quite possibly) stun yourself a little. Last thing you need in a gunfight is to lose ALL of one of your primary senses.

A 5.7x28 out of a PS90 will still do this, it's by no means hearing safe when shot indoors unless you SBR it and throw a Gemtech on it, but in stock form it's still nowhere NEAR as loud as a 223 fired from a 16" AR.

mavracer
July 9, 2014, 12:52 PM
A 5.7x28 out of a PS90 will still do this, it's by no means hearing safe when shot indoors unless you SBR it and throw a Gemtech on it, but in stock form it's still nowhere NEAR as loud as a 223 fired from a 16" AR.
Actually if you don't cherry pick data they really aren't that far apart.
In FN's testing the 5.7 was 161 Db, a 16" M4gery with a A2 flash hider is only 162 Db Now if you compare a big 3 gun brake you can get to 165 and above but I wouldn't suggest that for SD.
I'd suggest a linear comp which will drop a 16" AR below 160.
Also just a point of reference DB's scale isnt linear and a 170 Db flash bang is twice as loud as a 160 Db muzzle blast. and just for the record 170 is at the edge of the 5 meter effective range of a FB at 1 meter it's 180

barnbwt
July 9, 2014, 10:25 PM
A cursory Google search...
http://www.sadefensejournal.com/wp/?p=1093
http://sadefensejournal.com/wp/wp-content/uploads/2012/02/barrel5.jpg
http://sadefensejournal.com/wp/wp-content/uploads/2012/02/barrel6.jpg
Only a sample of one, but far more scientifically documented than any other study I've ready through on 223.

I can't seem to find such quantified data on 5.7 (also, Quickload apparently sucks at modeling that cartridge) so it's harder to make a direct comparison, but;
-We appear to be talking more like 2200 ft/sec for a 7" barrel, and rapidly dropping at that
-Notably, a 5" barrel is well below the ~2000ft/sec from a five-seven pistol, with a projectile going way slower than designed
-17000psi from a 7" barrel, and seeing how 5.7 is 20% lower pressure to start, and has like 1/3rd the case capacity & powder charge, we can surmise both pistol and carbine have markedly lower pressure than the corresponding 223 numbers.
-For sub-50 grain projectiles, can we at least agree that velocity is the only real number worth looking at for the purposes being considered (i.e. not hunting deer)?

Anywhoooo...all this to simply make the point that the cartridge isn't what we need to be debating for this particular application (plinking, defense, light varminting, general utility). So...as far as the actual platforms that can be debated as far their merits, we only have a few choices;

-AR57
-MPA57
-P90

At least, unless someone besides Masterpiece Arms is making a 5.7x28-anything.

TCB

barnbwt
July 9, 2014, 10:31 PM
In FN's testing the 5.7 was 161 Db
I don't suppose that was from the pistol, was it? I'm just trying to understand the physics of such a smaller-volume, lower-pressure round of the same diameter being anywhere in the same ballpark as 223, as far as muzzle pressure (blast loudness) is concerned :confused:

TCB

MachIVshooter
July 10, 2014, 12:08 AM
I'm just trying to understand the physics of such a smaller-volume, lower-pressure round of the same diameter being anywhere in the same ballpark as 223, as far as muzzle pressure (blast loudness) is concerned

dB are in no way directly related to pressure. dB is a logarithmic expression of noise intensity; frequency, pressure, and duration are separate components (no less important). Low dB noises with high pressure can just as easily damage hearing. Likewise, sounds of the same dB rating may be perceived as more intense if the duration is longer (can you imagine a 5 second long gun shot?).

Case in point, a .50 BMG has about the same dB rating that many large magnum rifles produce (about 175), but the quantity of propellant equates to a blast that you can feel considerably further away. Top alcohol dragsters are in the same range, and you can feel that pressure on your chest from well over 100 feet away (and nitromethane dragsters can hit 210 dB! :eek:). Remember, every 3 dB is a DOUBLING of intensity.

Cooldill
July 10, 2014, 12:24 AM
I frankly do not care HOW loud a gun is for HD.

To me, like my buddies (many in the SPECOPS community), an SBR tac carbine makes perfect sense for HD work. Extremely compact, manuevearable, massive stopping power vs. any handgun round, room for optics/lights/etc. etc. etc., it pretty much has all basis covered in that role IMHO.

Listen, ALL guns are going to be loud fired indoors. ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.

IDK about you, but I will NOT step down to any lesser weapon system than an AR for HD. I would certainly prefer something with about an 11.5" tube, but right now my 16.5 should work fine. Just because it's a little more noisy than some systems doesn't mean I won't use it, because it is the BEST option available in an HD platform time now.

JMHO.

YMMV.

MachIVshooter
July 10, 2014, 12:37 AM
I frankly do not care HOW loud a gun is for HD

You may feel differently if you ever have to use it.

Have you ever fired a rifle, even a 16"+ tube, inside the confines of a 100-150 sq ft. area? It's startling, even with ears on and in full anticipation. That overpressure is confined; you really feel it. Not vastly different from the concept of a firecracker on an open palm vs. clasped in a fist. Even absent perceptible noise, pressure can easily damage hearing. The tympanic membrane is not very tough; just ask anyone who's had their ears boxed. If they had it happen under water, you may have to ask them in writing or ASL.

ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.

Look, the dB level of any firearm other than a .22 rifle is well above the threshold of instant and permanent hearing loss.

I'm not saying you shouldn't use a rifle for HD, just be aware of the damage it may do, and take appropriate measures. I, too, keep a 12.5" SBR AR in 5.56mm for HD. I also have a set of electronic muffs right next to it. My 10mm handgun is a primary for investigating noises or if I were to literally wake to a BG in the doorway. It will definitely hurt my ears, but burning 60% less powder and at just a bit more than half the pressure, is nowhere near as offensive as a 5.56mm SBR. If I have time to get the rifle into action, I have time to get the muffs on.

barnbwt
July 10, 2014, 12:56 AM
frequency, pressure, and duration are separate components
They do correlate to each other, though; barrel volume to frequency, duration to 'overbore'/excess case volume and also gas velocity (which in turn is related to pressure), pressure at the muzzle is arguably correlated to powder volume as well (supposedly all powders generate roughly the same volume of gas, from what I've read).

Frequency should be the same, seeing as same bore, same barrel length (for 16" carbine). Pressure is markedly higher in the AR in all lengths; I honestly wonder if the 5.7 isn't getting close to ambient after 16". Duration favors the AR as well, owing to it's larger case volume.

There is one factor that goes unmentioned, though, and that is the overpressure bubble. When a super-sonic high pressure round is fired, a spherical bubble of super-sonic gas is forced from the muzzle, vectorable to a degree by compensators. The boundary of the bubble is a pressure discontinuity or shockwave, with higher pressure air on one side and ambient on the other, with no gradient between them. It is literally like having your ears boxed by a palm if it is large enough to engulf your person; there is bulk force involved due to the pressure differential. Even a super short 223 can generate enough velocity to get the gas bubble formed at the muzzle, and the size of the bubble is directly proportionate to the mass of expanding gas inside the bubble (or pressure & temperature, if you will). The more powder generating the bubble, the farther it can expand before the pressure inside is the same as ambient, and the pressure wave coalesces into a mere sound wave. At the same time, the shorter the barrel, the closer you start to the bubble in the first place.

SBR tac carbine makes perfect sense for HD work. Extremely compact, manuevearable, massive stopping power vs. any handgun round, room for optics/lights/etc. etc. etc., it pretty much has all basis covered in that role IMHO.
Again, this is simply not quite the case in short AR's (sub ten inch). This is common knowledge in even the NFA forum, here, never mind the brief research I did on the subject today.

ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.
I'm afraid you would likely be wrong. Remember that hearing loss isn't the problem, but tinnitus; it's driven people to suicide, and is not something to take lightly. FWIW, hearing loss is probably one of, if not the most common injury sustained by our servicemen, and I for one have never understood why suppressors are not more common, nor electronically filtered/enhanced earplugs mandatory in training and hostile areas by this time. I mean, considering how much money we waste on hearing aids after the fact, and all...

"Malp...Malp...Malp... --Sterling Archer

TCB

MachIVshooter
July 10, 2014, 02:34 AM
They do correlate to each other, though; barrel volume to frequency, duration to 'overbore'/excess case volume and also gas velocity (which in turn is related to pressure),

Absolutely true. I only aimed to point out that there is no consistent general equation for dB:PSI/kPa

pressure at the muzzle is arguably correlated to powder volume as well (supposedly all powders generate roughly the same volume of gas, from what I've read).

Yes, it would be. And yes, smokeless powders, as a rule of thumb, expand to 14,000 times their volume as a solid. I would point out, though, that you have to account for barrel length. All else being equal, a barrel that continues to house the bullet for a longer period of time is going to result in the pressure attenuating further before the projectile exits the muzzle. This is one of the basic principles behind suppressors as well; contain, vector and attenuate the blast to keep a significant portion of it from exiting.

Powder burn rate can, of course, affect this, most notably with handguns; if the powder does not burn completely before the bullet exits, you may have unburned powder exiting the muzzle. If it never burns, it never expands to gas, hence less total pressure. But that is really inconsequential and academic minutia.

Frequency should be the same, seeing as same bore, same barrel length (for 16" carbine). Pressure is markedly higher in the AR in all lengths; I honestly wonder if the 5.7 isn't getting close to ambient after 16". Duration favors the AR as well, owing to it's larger case volume.

Honestly don't know enough about acoustics to speculate about the frequency aspect. I would surmise, though, that myriad factors come into play there, including barrel harmonics, air density, temperature, and so on.

I also don't know that the volume directly correlates with the duration, though I'm inclined to agree with your theory.

There is one factor that goes unmentioned, though, and that is the overpressure bubble. When a super-sonic high pressure round is fired, a spherical bubble of super-sonic gas is forced from the muzzle,

That's not exclusive to super sonic rounds; All smokeless powders expand at a super sonic rate. The component that is unique to super sonic rounds is the sonic crack the bullet produces.

The boundary of the bubble is a pressure discontinuity or shockwave, with higher pressure air on one side and ambient on the other, with no gradient between them. It is literally like having your ears boxed by a palm if it is large enough to engulf your person; there is bulk force involved due to the pressure differential. Even a super short 223 can generate enough velocity to get the gas bubble formed at the muzzle, and the size of the bubble is directly proportionate to the mass of expanding gas inside the bubble (or pressure & temperature, if you will). The more powder generating the bubble, the farther it can expand before the pressure inside is the same as ambient, and the pressure wave coalesces into a mere sound wave. At the same time, the shorter the barrel, the closer you start to the bubble in the first place.

I concur with all but the highlighted portion. Pressure does not make sound, and sound is not a pressure wave. Sound is vibration, which is a change in pressure at a frequency. Air at 1 bar (atmosphere @ sea level) is silent, as is air at 10, 20, 100 atmospheres. Which is why your charged compressor in the garage makes no noise (unless it's leaking). But create changes in pressure, you get noise, such as that obnoxious pulsating when your car window is at just the wrong height going down the road.

But again, pressure and sound do not have a fixed relationship that is easily quantified. Smacking a piece of 1/4" sheet steel with a ball peen hammer is far more painful to the ears than the thud of a bass drum, but creates far less pressure. Conversely, that pulsating pressure created by the partially open car window is painful to your ears, but at a dB level that would be completely tolerable absent the high pressure component.

The science of acoustics is very interesting, and admittedly one that I need to spend a whole lot more time on. Far more complex than most people ever care to discover, for sure. To most, noise is either pleasant or it's not, and they don't really care about the why.

B!ngo
July 10, 2014, 03:24 AM
I think the contributors here covered all of the bases (even when there aren't bases!) but for me my real draw for the round was:
The PS90 itself is the coolest PDR ever created - for HD, short ranges, high-volume conflagrations. You lose all of the cool and much of the small, maneuverable, high-volume with the AR
The round is more interesting if you have the carbine and the FiveSeven so if you don't buy both, then the range toy value is reduced
Whenever you say 'range toy', the answer should always be 'yes' because the term overrides most practical considerations and turns in to an emotional one. Which is not bad at all - and is not meant as a diss. It's just different than, 'tell me which gun will more likely save my family's life?'.
I say do it, but reconsider the PS90 instead and plan on a FiveSeven in the future. And dollar-cost-average your way in to a good stock of ammo.
B

mavracer
July 10, 2014, 04:08 PM
I don't suppose that was from the pistol, was it?
Nope it was a P90 10.4" barrel and they said bare but I'm not sure if they had the factory A2 flash hider or not.
I'm fine with my 16" AR with a linear quiet brake, It may not be perfect situation but it does push most of the sound and blast toward the target. If I had a PS90 it'd wear one too.

4thPointOfContact
July 10, 2014, 05:12 PM
As a PS90 owner - -
I'm rather fond of the 5.7 round for indoor and short-range outdoor protective situations. The small caliber, high velocity round is more likely to break up upon encountering walls than is something like a 9, 40 or 45.

That said, I've also handled a 5.7 upper on both semi and full-auto AR lowers. It loses a little bit in handiness due to the increased weight over the P/PS90 platform*, but if you already have a lower then getting an upper is the lowest cost way to get the caliber. Another possible plus is that by inserting a magazine with the feed lips (mostly) removed, you can hold a full 50-rounds and keep them from getting underfoot.


* most of which was gained back on the full-auto as it had a shortened barrel. Most of the weight is probably in the monolithic Picatinney-railed upper. I wonder what it would weigh if M-loc or KeyMod instead.

barnbwt
July 10, 2014, 07:34 PM
Nope it was a P90 10.4" barrel and they said bare but I'm not sure if they had the factory A2 flash hider or not.
My five-seven pistol only has a 5" barrel and shoots the same round; I wonder why it isn't louder than a 16" AR15? :confused:

Meanwhile, my AR70 w/ Beretta slotted FH has a 17.75" barrel and seems louder despite the distance, plugs, and muffs. I must just be perceiving the increased recoil.

BTW, I did some paint mockup, and wow; the AR57 SBR on an SCR chassis does look pretty darn compelling. I sure hope it's actually doable. To think that little thing has the same firepower as something as large as a Thompson w/ 50rnd drum (let's please not debate "but it's a 45" with regards to a select fire bullet hose; it was always the number of shots on target that was important for a Thompson, same as a P90. When multiple hits are a given, the practical differences between cartridges become even more meaninigless)

TCB

browningguy
July 10, 2014, 09:55 PM
Mine is extremely accurate and gets used often for plinking and varmint shooting at night. Lovely gun with essentially zero recoil.

mavracer
July 10, 2014, 10:47 PM
My five-seven pistol only has a 5" barrel and shoots the same round; I wonder why it isn't louder than a 16" AR15?
I doubt that it isn't unless you're shooting AE ammo that stuff is pretty weak and prolly not as loud.

justice06rr
July 11, 2014, 02:38 AM
I think the 5.7 is great in a pistol like the FN57. In a M4 config like the AR57 upper, its a cool range toy IMHO.

The only real advantage of the AR57 is that 50rd mag, which is technically a wash if you use large capacity AR mags like the Surefire60 or any drum mag with a standard M4.

If you want it purely for plinking, then go for it.

But if you want more effective SD/HD with a little bit longer range capability, stick with 5.56.

ClickClickD'oh
July 11, 2014, 09:45 AM
I doubt that it isn't unless you're shooting AE ammo that stuff is pretty weak and prolly not as loud.

About 70 fps slower:

FN SS197SR 5.7x28mm 40gr
FN Five-Seven: 1839, 1849, 1838, 1833, 1823
Average: 1836 Spread: 26

Federal American Eagle 5.7x28mm 40gr
FN Five-Seven: 1790, 1783, 1748, 1752, 1745
Average: 1763 Spread: 45


That's what I got when I was running a large selection of ammunition over my chrony a couple weeks ago.

Trent
July 11, 2014, 10:44 AM
Click - what's the FPS difference out of a 16" tube?

Oh wait, I've already done that. :)

Federal American Eagle:
Low: 2008 FPS
High: 2113 FPS
Avg: 2075 FPS

SS197SR:
Low: 2041 fps
High: 2099 fps
Avg: 2083 fps

Source http://www.thehighroad.org/showthread.php?t=739404

It's negligible.

ClickClickD'oh
July 11, 2014, 10:55 AM
Now that's interesting with the Five-Seven showing a significantly larger variance. I wonder if the AE stuff is using a slower burning powder than the FN stuff.

Trent
July 11, 2014, 11:02 AM
They have to be, Click. The Extreme Spread difference also confirms it's a different powder; much higher on the AE ammo. Another tidbit; AE doesn't use glued in bullets or primers like Fiocci does. Another indication they are using a slower powder.

I saw the same thing with longshot. REAL nice velocities out of the PS90 (zooming right past factory ammo speeds, with no pressure signs); but it wasted unburnt powder out of the pistol. No matter how much you cram in to the case on a Five Seven, velocity stalls out at a certain point. Do the same thing in the rifle and you burst cases and pop primers. Powder is burning completely in the rifle, instead of venting.

Which brings me to the simple, unalterable truth about the 5.7 ... the ammunition is a compromise. It's why it took them so long to get a functioning handgun after developing the rifle. They had to re-engineer the ammunition and this took a while. :)

Because the actions are straight blow-back, you MUST have a very specific peak pressure and pressure curve in order to make them function properly and reliably. The only way to do this in a 3.7" vs. 13.6" tube (lengths comparing rifled area on Five Seven vs. PS90) is to compromise on the powder burn rate. It's the only way you can possibly get the action to release at the proper time, and with the proper force. The Teflon coating on the cases (plus glued in bullets and primers) also probably got added at a later time, to aid the extraction as they moved to a hotter powder to get the pistol to function properly, accelerate the burn curve a little, and keep primers from popping out.

Now all of this is speculation but it was done after a great deal of thought reverse engineering the how and why of the interior ballistics.

What this means to the casual shooter / reloader is you can develop some *really* nice high velocity rounds for the PS90, if you forego cross compatibility in to the pistol. I'm talking several hundred feet per second over factory, without pressure signs.

Which obviously changes the exterior ballistics, and stretches the range of that compact little gun that much further. A few hundred feet per second is nothing to sneeze at. :)

ClickClickD'oh
July 11, 2014, 11:08 AM
...plus glued in bullets and primers...

Funny story about that. I once watched a friend try to use a 5.7x28 round to demonstrate his nifty new inertial puller.

*whack* *whack* *whack* *whack* ***? *whack* *whack* *whack*

Just didn't have the heart to tell him the bullet was glued in place.
*whack*

mavracer
July 11, 2014, 11:18 AM
The more I read about the performance of the 5.7 and the saga of trying to reload it the less interesting the 5.7 becomes.
Click are those velocities actually from your Five seveN pistol? because that's a good 100 fps faster than any other reports I've seen.

ClickClickD'oh
July 11, 2014, 11:23 AM
Yes, those were shot from my Five-Seven over a Shooting Chrony F-1 on a 87 degree day.

Trent
July 11, 2014, 11:27 AM
Funny story about that. I once watched a friend try to use a 5.7x28 round to demonstrate his nifty new inertial puller.

*whack* *whack* *whack* *whack* ***? *whack* *whack* *whack*

Just didn't have the heart to tell him the bullet was glued in place.
*whack*

LOL! Yeah they've got to be seated deeper to break the glue first. Otherwise, you're peeing in the wind. :)

Decapping Fiocci 5.7 brass is fun. PIIING! ZIIIIIING!

Those sessions need little exploding "BANG! ZOOM!" cut scenes like the old batman series. It's actually kid of fun.

Trent
July 11, 2014, 11:33 AM
The more I read about the performance of the 5.7 and the saga of trying to reload it the less interesting the 5.7 becomes.
Click are those velocities actually from your Five seveN pistol? because that's a good 100 fps faster than any other reports I've seen.

LOL As anti 5.7x28 as you've been in this thread, it doesn't sound like you were too interested in the first place. :)

FYI velocity will change with temp / etc.

The figures I posted from the PS90 lacked environmental data, but they were shot in January 2014 when it was 14 degrees out (Farenheit). Real nasty frigging day. It's quite possible those would be much higher now that it's 90+ F outside, and it might even cause some previously safe loads to show pressure signs, rupture primers, etc.

The powder we are using isn't like high grade rifle powder (such as hodgedon extreme line, etc). It's temperature and positional sensitive. Powder forward/ powder back in the case can dramatically change pressures.

I'm going shopping today to see if I can find some of the new CFE Pistol powder, to start another round of testing on. On paper, at least, it's damn near perfect for the 5.7x28 (in pistol form.)

It's about midway between True Blue (great for pistol) and Longshot (great for PS90), so maybe a better compromise in there, if the bulkiness and burn curve are good. And if it doesn't work out? I'll use it in 9mm or 45. :)

mavracer
July 11, 2014, 11:41 AM
LOL As anti 5.7x28 as you've been in this thread, it doesn't sound like you were too interested in the first place.
Actually at one time I was hot on the trail of a Five Seven and I do believe that the P90 is a good system for a very small nitch. It's just that the voice of realism chimes in and says there's better choices to be made.

Trent
July 11, 2014, 11:55 AM
Actually at one time I was hot on the trail of a Five Seven and I do believe that the P90 is a good system for a very small nitch. It's just that the voice of realism chimes in and says there's better choices to be made.

Oh I dunno about a small niche. It's the go-to gun for 5 of 6 shooters in my house.

http://i.imgur.com/HokRoBAh.jpg

And the 6th (me) wouldn't feel at all uncomfortable or undergunned out to 200 yards.

Even with factory ammo, putting shots on target with the non magnified factory optics is simple at that distance.

http://i.imgur.com/WMhYNNNh.jpg

Feel free to use that as a reference point to gauge spin drift and drop w/ factory ammo. I held to the top edge of the bull at 200 yards. That was shot during a High Power sporting rifle match - which I won... gun is FANTASTIC to shoot out to 200 yards standing, and much more stable and MUCH faster to get on target than AR-15's.

Something worth considering; in the 200 yard High Power sporting rifle competitions I've been in, the score I laid down that day in the 80 shot course with the PS90 was never beaten.... by ANYONE.. last year, regardless of what system they used.

That factory-stock PS90 beat the scores I laid down the previous month in High Power sporting rifle, with a SCAR17S, and with an FN-AR w/ Leupold glass and a bipod.

That factory-stock PS90 beat the scores I put down with the H&K SL-8 the month following.

That factory-stock PS90 beat the scores I laid down with my match AR-15 w/ air gauged barrel chambered in wylde 223.

The ONLY place it got whooped up on was midrange prone - that PS90 just doesn't have the oomph to reach out 300+ yards. (I tried, and got a crappy 147/200 string at 300, whereas my AR15/SCAR17 scores are 170/190+).

If you have a PS90 in your hands and know how to use it, ANYTHING under 200 yards that is a threat simply won't BE a threat to you for very long.

bikemutt
July 11, 2014, 12:36 PM
I saw a couple YouTube videos showing a guy shooting an FN 57 pistol adorned with a Guardian 22 suppressor. I happen to own a G22.

The video does state that the G22 is only suitable for use with the 57 pistol and not the carbine because there is too pressure with the carbine.

So, I got to thinking, the AR57 also comes in a cool-looking 6" barrel which is completely covered up with the forearm. The idea is a suppressor that's under 1.25" in diameter (the G22 is 1") fits inside the forearm attaching to the recessed muzzle.

An FN 57 pistol has a barrel length of 4.8", that's 1.2" shorter than the AR57's 6" barrel: Would the pressure be significantly more with the 6" barrel compared to 4.8" barrel?

Thanks.

Trent
July 11, 2014, 12:48 PM
An FN 57 pistol has a barrel length of 4.8", that's 1.2" shorter than the AR57's 6" barrel: Would the pressure be significantly more with the 6" barrel compared to 4.8" barrel?

Thanks.

It depends on powder.

That Longshot powder I was using, for instance, has a peak burn rate curve just beyond the length of the standard Five Seven barrel. It *would* - with no doubt - cause dramatically higher pressures at the muzzle in a 6" barrel than a 4.8" barrel. That extra 1.2" is all that is needed to realize the rest of the potential.

Not knowing what powder the factory uses, and not having access to a pressure test barrel or equipment to measure port pressure at various distances, I can't give you an answer because it would be pure speculation.

Is it possible? Oh heck yeah.

Does that mean it's going to be an issue? No idea.

bikemutt
July 11, 2014, 12:53 PM
It depends on powder.

That Longshot powder I was using, for instance, has a peak burn rate curve just beyond the length of the standard Five Seven barrel. It *would* - with no doubt - cause dramatically higher pressures at the muzzle in a 6" barrel than a 4.8" barrel. That extra 1.2" is all that is needed to realize the rest of the potential.

Not knowing what powder the factory uses, and not having access to a pressure test barrel or equipment to measure port pressure at various distances, I can't give you an answer because it would be pure speculation.

Is it possible? Oh heck yeah.

Does that mean it's going to be an issue? No idea.
Thanks Trent.

If I could fit my 30 cal can down that forearm I'd use it sub-caliber, not happening, too fat.

mavracer
July 11, 2014, 02:26 PM
If you have a PS90 in your hands and know how to use it, ANYTHING under 200 yards that is a threat simply won't BE a threat to you for very long.
You guy's keep making these bold statements, that just a little fact checking draws some heavy sighs from a thinking man.
At 200 yards that little 40gr bullet is now barely supersonic and is below the velocity that many 22lr rounds produce and has just a bit over 100 ft lbs of energy according to Federal's ballistic tables which start at a claimed velocity of 2250 which you didn't see in the real world.

Trent
July 11, 2014, 03:21 PM
You guy's keep making these bold statements, that just a little fact checking draws some heavy sighs from a thinking man.
At 200 yards that little 40gr bullet is now barely supersonic and is below the velocity that many 22lr rounds produce and has just a bit over 100 ft lbs of energy according to Federal's ballistic tables which start at a claimed velocity of 2250 which you didn't see in the real world.
Speed of sound at 70 degrees Farenheit is 1128 feet per second.

(http://www.engineeringtoolbox.com/air-speed-sound-d_603.html)

Running a 40gr bullet at 2100fps (what I clocked factory ammo at this January), at 70 degrees farenheit shows ...

http://i.imgur.com/XK3QHukh.png

... that it stays supersonic to TWICE that distance - 400 yards, or close to a quarter mile. It's also packing "more than 100 ft/lb" out to 375 yards.

At 200 yards it's hitting with 181ft/lb of energy, well over 1.5x more than a standard velocity 22 at the muzzle. It's enough to turn that 40 gr Hornaday projectile in to a very nasty wound.

It's still pushing as much energy as a 5.56 round shooting 55gr projectiles @ 3200 fps is at 600 yards, and those are still PLENTY lethal at that distance.

Like I said earlier, there ARE limits obviously; the trajectory curve after 200 yards sucks (11" of drop at 200 vs. 37" of drop at 300, which makes it damn hard to compensate for with non-magnified red dot optics.)

mavracer
July 11, 2014, 04:10 PM
As I said that was off the Federal Website, so the SS197sr is a bit better now you're solidly in the hyper velocity 22 lr power at 200. Yawn If somebody is shooting at me from 200 yards I'd rather not try to hit them with something I'd use for rabbits if I have a choice.
AND I DO.
BTW it's not supersonic at 400

Sun Tzu warrior
July 11, 2014, 04:31 PM
Walkalong, "Too bad there isn't one readily available in .22 Mag."
There is, here is a link; http://www.ray-vin.com
Those who have them over on rimfire central speak highly.
STW

MistWolf
July 11, 2014, 05:09 PM
The video does state that the G22 is only suitable for use with the 57 pistol and not the carbine because there is too pressure with the carbine
No...


...Would the pressure be significantly more with the 6" barrel compared to 4.8" barrel?
...no...

It depends on powder.

That Longshot powder I was using, for instance, has a peak burn rate curve just beyond the length of the standard Five Seven barrel. It *would* - with no doubt - cause dramatically higher pressures at the muzzle in a 6" barrel than a 4.8" barrel. That extra 1.2" is all that is needed to realize the rest of the potential...
..and no. The further the bullet travels down the barrel, the more the pressure drops

bikemutt
July 11, 2014, 06:37 PM
Walkalong, "Too bad there isn't one readily available in .22 Mag."
There is, here is a link; http://www.ray-vin.com
Those who have them over on rimfire central speak highly.
STW
Wow, who knew?

Thanks for the link.

bikemutt
July 11, 2014, 07:33 PM
No...



...no...


..and no. The further the bullet travels down the barrel, the more the pressure drops
Please forgive my ignorance on the matter but, if what propels a bullet is pressure and it's well known that the same bullet exits a rifle with significantly greater velocity that a pistol, how could the pressure in the rifle barrel be less?

Trent
July 11, 2014, 08:42 PM
..and no. The further the bullet travels down the barrel, the more the pressure drops

Incorrect... powder burn is in a curve and peak pressure is definitely not always at the throat.

barnbwt
July 11, 2014, 09:21 PM
I'm pretty surprised, too, since 5.7 has such fast powder and so little of it, and a rifle primer, to boot. As small as it is, it seems hard to imagine it is very overbore. Has anyone actually plotted a pressure curve for 5.7? I looked into it, since I'm trying to design a gas-operated 5.7x28 carbine, and found that Quickload is apparently horrible at predicting max pressures (and in the unsafe direction, too :eek:). I think you could back out the data using measured velocities for progressively-shorter barrels, but you'd still have a hard time capturing the peak of the wave which would be very near to or past the chamber throat.

What may be muddying the issue is that powder burn and pressure won't necessarily correlate, since the chamber volume is changing so radically relative to the case size. Powder could still be burning, but the bullet already driven fast enough by the initial pressure spike that pressures continue to drop. I'm pretty sure you'd need super-delayed two-stage powders to both drive the bullet down the pipe, then drive pressures higher (but that's not the same thing as 'burn rate'). I have no idea how burn rate is calculated or simulated, but I know it can't be measured as easily as pressure, which is I thought why most internal ballistics works on pressure figures.

That Longshot powder I was using, for instance, has a peak burn rate curve just beyond the length of the standard Five Seven barrel. It *would* - with no doubt - cause dramatically higher pressures at the muzzle in a 6" barrel than a 4.8" barrel. That extra 1.2" is all that is needed to realize the rest of the potential...
I thought for sure you originally meant velocity rather than pressure. I fully expect that velocity is most efficiently generated right around the length of the pistol that was designed with/around the cartridge. I also understand how the slower-burning round slated for the carbine would have trouble transferring sufficient energy in the 1/3rd length barrel of the pistol, drastically limiting its effectiveness.

Please forgive my ignorance on the matter but, if what propels a bullet is pressure and it's well known that the same bullet exits a rifle with significantly greater velocity that a pistol, how could the pressure in the rifle barrel be less?
In most (all?) other pistol cartridges, the powder is almost fully engulfed before the bullet has moved much at all, or is in the process of burning. Between the decomposition into gas components and super high temperatures also generated, this is when pressures peak. After this point, the chamber volume increases as the bullet moves away, and there is no more powder to burn and generate gas volume and heat; the result is pressures and temperatures drop rapidly. A shorter barrel can't drop as much as a longer rifle barrel before the muzzle opens, but that doesn't mean huge pressures aren't still accelerating the bullet. Even though pressure may have dropped to only a few thousand psi at a long muzzle vs. a short one, there's still hundreds of pounds bearing on the bullet (and rifling only saps about 100lb from that).

To correlate the pressure curve to velocity, you need the integral, or sum, of pressure times area (force) on the bullet for the duration it's in the bore. A rifle drives a bullet longer, with decreasing force, so the net energy imparted is more than a truncated section of the same curve you'd get from a pistol. Eventually, pressures drop enough that the bullet slows down (like 9mm from a 16" barrel, IIRC) but are still high enough to make noise once uncorked --not much though.

TCB

MistWolf
July 11, 2014, 09:30 PM
Physics disagrees, Trent. Peak pressure occurs where the bullet meets the greatest resistance and that's where it begins it's journey in the rifling.

bikemutt, as the bullet travels along the barrel, the volume increases. As volume increases, pressure decreases. Pressure also decreases because the gasses are also losing heat. The reason the bullet comes out faster is because the gas, without anything to restrict it's speed, expands at a constant velocity of about 5700 feet per second. The speed and pressure accelerates is constantly accelerating the bullet. Once the bullet gets going, there doesn't need to be as much pressure to keep accelerating it. It's that old Newtonian physics at work for ya- Objects in motion tend to stay in motion; Objects that are not in motion tend to stay motionless.

Here's another thing to think about- the mass of the gas is only about 23 grains or so- the mass of the powder charge

barnbwt
July 11, 2014, 10:44 PM
The speed and pressure accelerates is constantly accelerating the bullet.
I get your jist, but it's solely pressure that's driving the bullet (and gas) forward, and acceleration is continuous, but hardly constant (which is why a long enough barrel will slow a cartridge).

If and I say if, the 5.7 had super-duper slow powder that magically ignited and burned out at the same rate across the barrel length (making an arc-shaped plot of burn rate), we'd have something closer the situation of high pressures occurring near the end of the barrel length. But chemical kinetics (which I for sure don't claim to know hardly anything about) indicate conflagration should occur way, way faster than the taper off (I think it's like a fourth-power thing, if memory and chemical formulas are being remembered correctly) --almost instantaneous in comparison, in fact. So the actual internal ballistics is closer to the idealized scenario in which pressure is instantaneously peaked (necessarily at a higher-than-factual level) and drops precipitously as the bullet moves, quickly flattening out as the total volume increases and pressure approaches ambient.

As much effort as FNH put into the cartridge, I would not put a binary or variable-rate powder concoction past them, but evidence does seem to suggest the 'secret ingredient' is merely some really fast pistol powder.

TCB

MistWolf
July 11, 2014, 11:31 PM
I get your jist, but it's solely pressure that's driving the bullet (and gas) forward, and acceleration is continuous, but hardly constant (which is why a long enough barrel will slow a cartridge).
It's also the velocity at which the gas will expand. The projectile will always travel slower than the velocity at which the gas will expand freely.

You are correct about the technical definition of "constant rate". It would have been more correct if I'd said "continuously", but in my defense I did not say "constant rate" I said "constantly" :)

It is understood that, while longer barrels give more velocity because the gas has more time to accelerate the bullet, there is a point of diminishing returns. At some point, the gas can no longer accelerate the bullet and it will start losing velocity.

I couldn't find a pressure graph for the 5.7, but pressure graphs look very similar regardless of caliber-

30-06
http://www.shootersforum.com/attachments/ballistics-internal-external/9980d1296335107-pressure-curves-1-29-2011-4-03-17-pm.gif
http://accurateshooter.net/Blog/emaryammo01op.png

300 Winchester Magnum
http://oi55.tinypic.com/14icx28.jpg

38 Super
http://www.shootingtimes.com/wp-content/blogs.dir/11/files/compensators-pressure-or-gas/figure-5-compensators-pressure-or-gas.jpg

There is always a rapid rise and peak, followed by a parabolic shaped drop

bikemutt
July 12, 2014, 07:26 AM
MistWolf, thanks for explaining the underlying Physics of the matter.

Here's the YouTube video where the author shoots a 5.7 pistol with the Guardian 22 (G22) suppressor. The comment is where the pressure is mentioned: http://www.youtube.com/watch?v=XneDPIU2bD0

Published on Mar 29, 2012
Listen to the difference! I shoot with the suppressor on and off.
This is the Guardian 22 by Huntertown Arms in Indiana. This small, light .22LR suppressor works great on the 5.7 pistol. It will not handle a 5.7 cabine. Too much pressure.
Hear more Huntertown suppressors here:

On Huntertown Arms website they rate the G22 for 5.7 with an asterisk stating only serial numbers greater than a certain value are included. They don't qualify it further by barrel length but it's possible the rating was rendered before carbine length barrels materialized.

My suppressor's serial number indicates it may not be suitable for use with 5.7 but I've also sent mine in to have the aluminium baffles replaced with stainless steel, they also upgraded the end caps at no charge to current production ones. In other works, it's possible mine may now be OK to use with 5.7. I've left them a voice mail asking if my specimen is safe to use with 5.7 and if not, can it be upgraded to handle it. I waited so long for that suppressor I really don't want to blow the darn thing up, or myself for that matter.

barnbwt
July 12, 2014, 11:03 AM
It's also the velocity at which the gas will expand. The projectile will always travel slower than the velocity at which the gas will expand freely.

Yes, and why does the gas only expand freely so fast? Because the reacting propellant's energy/gas production can only generate so much pressure so rapidly (and you can't accelerate the bullet instantly, so to transfer energy to the bullet, it has to move, meaning the chamber volume has to increase rapidly --catch 22, which limits what we can do with nitrocellulose). Two sides of the same equation.

I personally think this is also why 4.6x30 (H&K MP7) is so much more inefficient as a cartridge; the bullet's are often the same mass as 5.7, since mass decreases slower with bore diameter at these itty bitty sizes, but can barely be driven to the about the same speeds by an even larger powder charge and higher pressure. It's like the opposite of a sabot.

TCB

Trent
July 12, 2014, 11:22 AM
Physics disagrees, Trent. Peak pressure occurs where the bullet meets the greatest resistance and that's where it begins it's journey in the rifling.

... Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?

To support what you are saying ALL of the powder would have to burn before the bullet starts moving, and it simply does NOT do that.

For hot pistol powders it may hit peak at .1" past the throat, but for slower powders that may be much further down the barrel; several inches.

E.g. pack a 45 ACP case full of H1000 (slow magnum rifle powder) and won't that pressure will still be ramping up (slowly) until the bullet falls out the end of the barrel? :)

dprice3844444
July 12, 2014, 11:54 AM
1. i think it would be a great setup for in house personal defense.enough penetration to get the job done,and less of a chance for over penetration like the hotter caliber.50 rounds,no reloading.
2.you can make a pouch setup under the mag well to catch the empties.

barnbwt
July 12, 2014, 12:58 PM
Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?

Doesn't win mag have a ton of extra powder relative to the barrel/chamber volume (over bore) that has to be burnt to reach peak pressure in the first place? Powder that is far, far slower than 5.7 would ever use in the first place? That extra time gives the bullet the chance to move further (albeit under less-than-peak pressures)

I agree that even a 5.7 bullet has likely shifted or even left the case by the time the powder has fully conflagrated, but not inches down the bore; not without extremely slow (think 'punky') powders that would probably never ignite well in the then-too-voluminous (low pressure) interior. Powder has to be closely packed to burn well, and you can't get that in a 5.7x28 if the bullet is inches down the barrel, doubling or tripling the initial case volume.

The other thing is that it'd be extremely difficult to measure and corroborate stuff happening in the first .1" of bullet travel; too much happening too fast for instrumentation to capture well.

All that junk said... Trent has done a ton of reloading and experimentation with the 5.7, so I imagine he has as much data as anybody out there, which is really all we have to work with since the little round's internal ballistics apparently can't be accurately modeled with software (yet). We really need to find someone with a chrono and a Contender in 5.7x28, so I can get a test barrel made that can be cut progressively shorter. If we can back the curve out to the first inch or so, I think that would tell us a lot about how the round does its thing, and what, if any, potential there is to be gained by reloaders or gun designers. But perhaps here's a reason all other duty-pistol cartridges have pistol barrels of ~5" and SMG barrels of ~10", just like the five-seven and P90 ;) (MP7 is 7", making it an unpleasant compromise of ballistics and flash/boom/inefficiency)

It may be moot in any case, since a pistol barrel shorter than 5" will only get louder and flashier than it is now, longer ones can't be carried easily, barrels under 16" for carbines won't find much of a market in any case, and I doubt there's much to be gained in going longer than 16" for such a small powder charge.

EDIT: The real solution for better performance from the carbine would be to get a smaller primer in the cartridge. At that point, the case head is strong enough for higher pressures, and the small bit of powder would still have plenty of time to burn from the now-weaker primer charge over the course of a 16" barrel. A 5.7x28 peaking at 60,000psi vs 50,000psi would climb to different heights than the present case allows. According to a fellow on barfcom who made a gas-op 5.7, increasing pressures much at all loosens the primer pockets and ruins the brass :(

TCB

barnbwt
July 12, 2014, 01:02 PM
like the hotter caliber.50 rounds
Wait, wut? :confused: You're not considering an AR50 upper, are you? :D

TCB

MistWolf
July 12, 2014, 01:23 PM
... Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?
Look at the pressure rise. If not for the restriction of the bullet entering the rifling, pressure would never rise like that. Neck tension isn't enough to hold the bullet to cause any real spike in pressure

To support what you are saying ALL of the powder would have to burn before the bullet starts moving, and it simply does NOT do that.[/qoute]
Not so. The primer by itself creates enough pressure to push the bullet out of the case and into the rifling

[quote]For hot pistol powders it may hit peak at .1" past the throat, but for slower powders that may be much further down the barrel; several inches.
Pistol powders burn too quick and pistol cases don't hold enough powder for that to happen

E.g. pack a 45 ACP case full of H1000 (slow magnum rifle powder) and won't that pressure will still be ramping up (slowly) until the bullet falls out the end of the barrel? :)
The slowest of pistol powders still have a quicker burn rate than the fastest of rifle powders.

When smokeless powder begins to burn, it does so rapidly. It makes very little pressure unless contained. Case neck tension alone isn't enough to allow pressure to build to any significant degree. When the primer is ignited, not only does it start the powder to burning, it also pressurizes the case and it's possible the primer will start the bullet before the burning powder has built enough pressure to push the bullet on it's own.

The bullet leaves the case but is stopped a short distance later at the leade where the throat meets the rifling. The bullet's acceleration is lowed at this point. More force is now required to push the bullet and pressure rapidly rises. Once the pressure gets the bullet accelerating again, pressure is relieved and begins to fall off. If there is enough powder behind the bullet, pressure can build faster than the increasing volume can relieve it which shows as a continued rise, but it is still falling off. You can see this phenomena in the pressure graph. The peak curve is much gentler, less sharp, than with smaller cases.

It's very important to understand this, especially as a reloader. If that spike rises too rapidly, even if it does not exceed maximum allowable pressure, it will cause a catastrophic failure. This is why quick burning rate powders are limited to small capacity cases. If used in a case too large, pressure will rise too rapidly.

We can see this work with seating depth. Bench rest shooters often seat their bullets so they are very close to or even touching the rifling when the round is chambered. There is very little to no bullet jump to slow the pressure spike. Powder charge must be reduced to keep the pressure rise from being too quick as well as keeping pressure within acceptable limits.

Roy Weatherby went the other way. He used long leades with his magnums to increase volume during pressure rise. This allowed the use of more powder for increased velocity while keeping pressure rise and peak pressure at safe levels

barnbwt
July 12, 2014, 04:54 PM
If that spike rises too rapidly, even if it does not exceed maximum allowable pressure, it will cause a catastrophic failure. This is why quick burning rate powders are limited to small capacity cases. If used in a case too large, pressure will rise too rapidly.
Fast powders (like blank powder, as an extreme example) burn so fast the chamber volume can not adjust via bullet movement fast enough to keep pressures from reaching dangerous levels. I'll need some explanation as to how the rate of application of the breech thrust itself would cause failure, though, since I'm not aware of 'jerk' (force derivative wrt time) having much effect on steel failure apart from fatigue acceleration. Even blank powder isn't a true 'explosive' that would put impact loading on the action.

I always thought Weatherby's had long throats so that a wide array of heavy bullets could be used safely?

I must say this is fascinating talk; we should really get the mods to split it off around post #64 or so :)

TCB

hso
July 12, 2014, 06:02 PM
:scrutiny:
as the bullet travels along the barrel, the volume increases

Yes

As volume increases, pressure decreases

That's true, but oversimplified for a system where the powder is still burning and contributing expanding gas to the equation.

Pressure also decreases because the gasses are also losing heat.

True, but irrelevant for a system as small as the rifle of a barrel and one in which the powder is still burning to produce expanding gas.

The reason the bullet comes out faster is because the gas, without anything to restrict it's speed, expands at a constant velocity of about 5700 feet per second.

:scrutiny:
Where's 5,700 ft./sec come from for the initial sound speed of the propellant? a0 may be the initial speed of the propellant, but the max velocity is still impacted by the friction of the bullet in the bore and the burning powder contributing against the increased volume of the bore.

The speed and pressure accelerates is constantly accelerating the bullet.

I'm not sure what "speed and pressure accelerates it(sic) constantly accelerating the bullet" means. The bullet is like a piston and the barrel is the cylinder. The powder burns causing expanding gas to push against the bullet. The bullet moves because the pressure overcomes the static friction of the bullet in the chamber and the first stage of the rifling. It accelerates from V0 in the chamber and continues to accelerate up to a point. A long as the pressure of the gases from the burning powder overcomes the sliding friction of the bullet in the barrel the bullet accelerates. At some point enough powder is burned where the pressure isn't increasing due to the increasing volume of the barrel and the end of the burn of the powder and the bullet MUST begin to slow against the sliding friction of the bullet in the barrel. A max velocity is reached and more barrel only slows the bullet as the pressure falls off much more rapidly with the increasing volume of the barrel and lack of expanding gases. This is why muzzle velocity for a longer barrel can be slower for the same round than a shorter barrel since the powder has burned enough for pressure to start to drop rapidly. If the pressure isn't maintained above a point to overcome the friction of the barrel the bullet can not accelerate and will begin to decelerate as the barrel friction slows the bullet.

Once the bullet gets going, there doesn't need to be as much pressure to keep accelerating it.

Yes, the static friction is much higher than the sliding friction and once moving the friction is less.

It's that old Newtonian physics at work for ya- Objects in motion tend to stay in motion; Objects that are not in motion tend to stay motionless.

No, but yes. Kinda :scrutiny: Newton's first law, Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it, is for uniform motion without external forces and a bullet in a barrel is anything but. The bullet's motion against the pressure of the expanding gases from the burning powder is opposed first by the static friction in the chamber. Once that is overcome it begins to move, but opposed by the sliding friction of the barrel. As long as the pressure from the expanding gases just exceed the friction forces on the bullet it will accelerate slowly, but the pressure is well above the frictional forces and the bullet accelerates rapidly. If the pressure was only from the initial pulse from the firing it would accelerate up rapidly and then rapidly slow (think squib) before leaving the barrel, but the powder burns for a period of time long enough to keep pressure against the bullet in the barrel until the powder burns and the volume in the barrel is too great. At that point the pressure falls off and eventually cannot overcome the friction. Too little barrel and the unburned powder burns outside the barrel wasting the energy on a bright flash and not accelerating the bullet and too much barrel causes the bullet to slow dramatically. It is not as simple as "good old Newtonian physics" by a "long shot". ;)

barnbwt
July 12, 2014, 06:32 PM
Although Newtonian physics (or rather, kinematics) do describe those things pretty well. I don't care to get into the stupidly-nitty-gritty as far as ballistics so close to the chamber that powder is burning, because that's in the realm of aerothermochemistry, a field I took an elective class on and learned enough to know I never want to think about it again. Hypersonic fluid dynamics combined with advanced chemical kinetics :barf:

I'm more interested in the useful figures that may be gleaned from analyzing the "end result" of the powder burn cycle, which in the case of 5.7 is likely not far beyond the throat at all for normal loads. Once the powder is at least no longer reacting, it's a lot easier to figure out the rest of an already complicated situation. No need to make a science project out of something that can be measured. I really will have to make a test barrel and get some SS197SR chrony readings in the process of my MP57 build, so that other makers might at least have some data to design competing platforms around and keep the round alive.

The more I learn about it, the more my opinion changes; I initially thought 5.7x28 had trouble taking off because FNH refused to license ammo production to other companies, but now I know that everything from making the ammo to designing new guns for it is incredibly difficult to do without having access to the extensive ballistics research data FNH doubtless had to generate for itself in the first place. If Quickload can't develop an accurate pressure spike, how is a company supposed to develop a competing platform without spending enormous R&D dollars duplicating that effort?

TCB

Trent
July 12, 2014, 08:16 PM
OK at this point I'm just along for the ride, interior ballistics master session in progress... :)

MistWolf
July 13, 2014, 12:30 AM
hso, heat does play into internal ballistics. A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.

I didn't say 5700 fps was the speed of sound, I said the speed of the expanding gasses for smokeless powder is a constant of about 5700 fps. You can research the subject and verify it for yourself. I believe it was a Lyman reloading manual where I first came across this fact. NOTE: One internet author claims the speed of the expanding gas is 5 times the muzzle velocity of the bullet. This is incorrect.

Having to overcome friction is part of Newtonian physics. Although there is friction between the bullet and the bore, if the bullet has enough momentum, it will continue to coast down the bore without pressure from the gas. Much like pushing a cardboard box full of books across a concrete floor. Because of the friction and the box being motionless (motionless object tends to stay motionless), you would have to push hard to get that box moving. But once it is moving, it takes less energy to keep it moving (object in motion tends to stay in motion). Get it moving fast enough and stop pushing, momentum will keep the box moving until friction stops it.

Just because it's rocket science, doesn't mean it's complicated

barnbwt
July 13, 2014, 09:11 AM
Mistwolf, as a 'rocket scientist' I can assure the process is anything but simple. Like all things, it can be broken into bite sized chunks and analyzed, or approximated as closely as we care to. But it's still a field, after 150+ years of study, that still isn't fully understood (seeing as we only recently discovered that short fat cases with sharply tapered necks are far more efficient than the long-neck brewsky of a 30-06.

I thought the 5.56 tumbling issue was due to cold weather not allowing the powder to react fast enough (so slower bullets) as well as the outside air being much colder (denser) which also has the effect of making the bullet behave like it is moving slower (same as how denser flesh causes it to tumble).

As fast as a bullet is fired, you'd think heat transfer would be nearly negligible as far as effecting ballistics, but the gasses are so hot that the same transfer happens really fast, too. It'd be interesting to see how much it really changes things (like if it would cause stringing as the barrel heats up), but my instincts tell me it is a pretty minor factor in most cases. 5.7x28 may not be one of those, however. In any case, all barrels are steel, making it a constant factor, but a ceramic bore might be far more efficient for all we know.

TCB

Trent
July 13, 2014, 09:31 AM
hso, heat does play into internal ballistics. A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.


I don't think that's a function of hot gas meeting barrel; I think that's due more to the powder *itself* reacting differently under lower temperatures.

Older, conventional powders are HIGHLY sensitive to cold, but that's not a function of flame temp interacting with bore. Good modern powders do not do that; my point of impact and velocity using H4831SC on 300 win mag did not change whatsover between -24F and 95F when I tested under both conditions this year, cold barrel or no, my first shot was dead on at the start of each string. Velocity did not increase, and the barrel did not walk, even when I was using it as a handwarmer.

http://i.imgur.com/NfZcG5Gh.jpg

If your theory about gas temps cooling were true, I couldn't put together a 20 shot 300 yard group (starting with a cold bore) at -24F without experiencing that phenomenon as the barrel warms from ice cold to blazing hot.

Clearly my wind reading skills need a bit of work, and I had one "whoops" shot fly high on shot 17 where the shivers made me jerk the trigger too early. :)

http://i.imgur.com/iteHFFjh.jpg

But there's absolutely no evidence that bore temp affects powder burn whatsoever, there. And if there WAS a scenario where bore temp was affecting powder burn, it'd be more evident on a long 24" barrel with slow burning powder, like I was using, than any other platform.

Some older powders burns slower when cold. If this phenomenon were due to the flame temp interacting with the bore temp *all* powders would do that and the velocity would increase as the barrel warmed. Even on the older powders you do NOT see that, unless you leave the cartridge in the gun to warm the *powder itself*. There's zero doubt that it's the *powder temp* that matters on those, as far as the effect it has on velocity.

Old Military powders (WC844, etc) are *horrible* when it comes to temperature sensitivity. But that has nothing to do with bore temp (otherwise the effect would wear off as the bore increased.)

If you pre-warm the cartridges (either by leaving them in a hot chamber for a spell, or against your body), the effect is neutralized, cold OR hot bore notwithstanding.

Sam Cade
July 13, 2014, 10:18 AM
A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.


That is completely wrong. 1:14 only marginally stabilized the projectile and wasn't enough to keep it point forward when it was passing though the denser arctic air.

If your theory was true once the barrel heated up the bullets would stabilize.

They didn't.


http://www.nennstiel-ruprecht.de/bullfly/gyrocond.htm

MistWolf
July 13, 2014, 10:24 AM
Actually barn, we have known for a very long time that the theoretically ideal combustion chamber is spherical with the ignition source in it's very center and that short, fat cases are closer to that ideal than long skinny cases. That's one theory as to why the 308 Winchester is inherently more accurate than the 30-06. But case shape is also affected by other requirements- magazine limitations; reliable feed, extraction and ejection and other considerations. I'm not saying all rocket science is simple, just that being rocket science doesn't automatically make it complicated :) As an Aviation Technician, I understand and appreciate that things can be broken down into smaller parts to simplify things. Trying to grasp how an entire jetliner works is over whelming. But taking one system- say the propulsion (engines)- and breaking it down into it's subsystems, components and the basic physics that makes it work, is a big start

The arctic cold did affect powder burn rate and air density but the loss of velocity resulted in enough loss of bullet rpm that stability problems showed up under those conditions.

Trent, powder sensitivity to temperature changes does play an important role in pressure variations just as you point out. British hunting calibers used in tropical conditions were large cased and low pressure (by modern standards) because the heat in Africa and India would cause unpredictable pressure spikes. Ammunition loaded to maximum pressures would give dangerous spikes from the heat.

A cold barrel pulling heat from the gas will have more affect on smaller capacity cases than larger ones because the larger cases hold more powder and produce more heat

MistWolf
July 13, 2014, 10:33 AM
Sam, there was also loss of velocity because of how the cold affected the powder. So it was a combination of things- reduction of RPM (due to velocity loss) and denser air plus the fact the 1:14 twist was marginal to begin with. Sapping heat from the gas is one factor, not the factor. All combustion driven engines (including firearms) operate more efficiently within a certain operating range. That why they work best when they reach operating temperatures but must be kept from overheating

Potatohead
July 13, 2014, 10:41 AM
Wow, this thread has gone sideways.

Trent
July 13, 2014, 03:25 PM
Wow, this thread has gone sideways.

Most threads on 5.7x28 platforms / ammo DO go sideways, and fast.

I'm just pleasantly surprised this one didn't result in any infractions, suspensions, or bans. :)

barnbwt
July 13, 2014, 05:06 PM
<deleted> But this is supposed to be an AR57 thread, so it'd be cool if mods would split it.

Trent, was your subzero ammo itself held to a set temperature, or was the powder as cold as the bore? It appears that at least for rifle power rounds, barrel heat transfer is negligence --I figured as much. I wonder if temp variance effects might be more profound in 5.7 for a number of reasons (namely, stability in the denser atmosphere)

TCB

Trent
July 13, 2014, 10:07 PM
<deleted> But this is supposed to be an AR57 thread, so it'd be cool if mods would split it.

Trent, was your subzero ammo itself held to a set temperature, or was the powder as cold as the bore? It appears that at least for rifle power rounds, barrel heat transfer is negligence --I figured as much. I wonder if temp variance effects might be more profound in 5.7 for a number of reasons (namely, stability in the denser atmosphere)

TCB

The powder on those shoots was as cold as the bore to start. The rifle and ammo both were allowed to acclimate to the outdoor temps slowly (to avoid frosting my scope lenses, that's a sure way to ruin your day, in subzero temps).

I hammered through the 20 shot strings in ~10 minutes or so, which is enough to seriously warm the 300 win mag barrel. Rounds were left in for varying amounts of time (depended mostly on sight picture, how long it took to calm me down from reloading, etc). The barrel warmed to the point it was hot to the touch (made a GREAT hand warmer wearing gloves, just grab the barrel and instant "ahhhhhh ooooooohhh".)

Powder that's temp insensitive just don't walk as the temp changes. If the BARREL has defects, it surely will walk as it warms. (why I sold my weatherby, thing was only good for 2 shots before it started walking off the paper.).

That krieger barrel I had put on my Savage rifle does NOT budge from point of impact though - no matter what I do to abuse it. :)

I didn't notice anything odd when I tested PS90 in cold weather in January. I shot it in temps down to 11F. It still shot just like it was summertime out. Didn't notice any point of impact shift with SS197 or AE ammo from when I'd shot it in matches that summer (in 90 degree weather).

barnbwt
July 13, 2014, 11:00 PM
Kewl. Sounds like modern powders really don't have an issue with cold weather (granted, hot weather most certainly does have an impact on pressure & therefore velocity levels, especially if storage is factored in). Kinda makes sense, because nitro-cellulose is a plastic, and plastics are pretty stable below their degradation temperature. Nitro is known to degrade increasingly rapidly above (IIRC) 90deg or so, and it reacts increasingly aggressively in +100deg temperatures. It's actually made me worry quite a bit for our guys in uniform; I've seen what happens to Kydex aircraft interior panels when they come back (think Pringles) indicating over 120deg temps in the aircraft that are supposedly looked after more carefully than random ammo crates.

(made a GREAT hand warmer wearing gloves, just grab the barrel and instant "ahhhhhh ooooooohhh".)
And that's how you frost a scope, right? :D What you need is a hot water bottle powered by a Vickers, and you can shoot in comfort all winter ;)

TCB

Ar180shooter
July 14, 2014, 05:32 PM
As a range toy:

I had one, and reloaded for it for a short time, but it just bored me. The caliber would be more fun/useful in a bolt gun or Contender IMHO. The upper was heavy for such a small caliber. I would just as soon shoot my .22 LR AR. Too bad there isn't one readily available in .22 Mag.

I enjoyed my 9MM AR a great deal more, it is simpler (A great deal simpler) to reload, factory ammo is cheaper, brass is plentiful.... I could go on and on.

As a range toy it simply did not make the cut. :)
What I'd love is a .17WSM AR-15. It would be the ultimate Coyote slayer.

Trent
July 14, 2014, 05:35 PM
What I'd love is a .17WSM AR-15. It would be the ultimate Coyote slayer.

Heck I'd like a 22-250 with those ergonomics. Talk about a -yote slayer. ;)

bikemutt
July 15, 2014, 11:58 AM
Here ya go...

http://www.franklinarmory.com/PRODUCTS.html

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